FAN CASING

Abstract: A fan casing comprises a duct (10) formed of a sheet material wrapped into cylindrical form, and a separate, rigid, ring-shaped flange (12) attached to each end of the duct. The flanges (12) impart rigidity to the fan casing and ensure concentricity for mounting an axial fan (14, 16), enabling the use of relatively thin metal or other material for the duct (10). Preferably the fan casing is secured to each adjacent duct or assembly (e.g. 1, 3) by means of a ring-shaped band having an inner pheripheral groove fitted over the flange (12) of the fan casing and a corresponding flange on the adjacent duct or assembly.

Description: Fan Casing The present invention relates to a casing construction for a fan, for example for a heating and ventilating system. Hitherto fan casings have been complicated and expensive to construct, in order to ensure accurate concentricity relative to the rotating fan. Thus, the casing has consisted of a sheet of thick-gauge metal which is formed into a cylinder of uniform diameter: the metal is thick enough to ensure that the cylinder will maintain its truly cylindrical shape. Then the opposite ends of the cylinder are bent outwards to form radial flanges, which are then drilled at intervals around their peripheries: these flanges serve for securing, by bolting, to similar flanges on the ends of ducts or other assemblies to which the fan casing is to be connected. Typically twelve bolts are employed for each mating pair of flanges, and take significant time and trouble to insert and tighten. We have now devised a fan casing of considerably less complicated construction and which, in one form, requires considerably less time and trouble to secure to the ends of other ducts or assemblies. In accordance with this invention, there is provided a fan casing which comprises a duct formed from a sheet of material wrapped into cylindrical form, and a separate, rigid, ring-shaped flange attached to each end of the duct. The rigid flanges impart rigidity to the fan casing and ensure concentricity: the arrangement therefore enables use of a relatively thin-gauge metal for the cylindrical duct of the casing. Preferably the fan casing is secured to the end of an adjacent duct or assembly by means of a ring-shaped band having an inner peripheral groove, and which fits over the flange at the end of the fan casing and over a corresponding flange on the end of the adjacent duct or assembly: this band can be tightened once placed in position, and enables assembly to be carried out very quickly and easily. Embodiments of this invention will now be described by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a longitudinal section through a fan unit mounted between two ducting assemblies; FIGURE 2 is an enlarged sectional view of a coupling between the fan unit and one of the adjacent ducts; and FIGURE 3 is a view similar to Figure 2, showing a modified embodiment. Referring to Figure 1 of the drawings, there is shown a fan unit 2 mounted between a flared inlet 1 and a duct 3. The fan casing comprises a duct 10 formed by a piece of relatively thin sheet metal which has been wrapped into a cylinder and had its opposite edges rivetted or welded together. The casing further comprises a rigid ring-shaped flange 12 rivetted to each end of the duct 10. The flanges 12 impart rigidity to the duct 10, to ensure concentricity relative to the fan blades. As shown, the fan impeller 14 is driven by an electric motor 16 which is mounted to a metal cross-member 18 having its opposite ends rivetted or welded to the duct 10, adjacent one end. In the embodiment shown in Figure 2, each flange 12 has a cylindrical portion 12a, from which a radially-outwards annulus 12b projects, the outer portion of the annulus 12b being bent inwardly again to form an inclined portion 12c directed towards the cylindrical portion 12a. The end of the casing duct 10 is joggled outwardly as shown to receive the flange cylindrical portion 12a, to which it is rivetted. In order to assemble the fan casing to the end of an adjacent duct 20 which has a similar flange e.g. 22, a clamping band 30 is used, having a groove around its inner periphery to fit over the two flanges 12, 22 as shown in Figure 2. The band is split at one point around its circumference, and the two ends are fastened together by a screw coupling which, upon tightening, secures the band around both the fan casing and the adjacent duct 20. Figure 3 shows a modified embodiment, in which the cylindrical portion 12a of each flange fits around the outside of the duct 10, instead of inside the duct 10 as in Figure 2; and the duct 10 is not joggled at its end. Although use of the clamping band is preferred, instead the flanges may be of L-section (i.e. consisting of portions 12a and 12b in the case of flange 12) , with the radially projecting portion (12b) drilled to enable mating pairs of flanges to be bolted together.

Claims: Claims 1) A fan casing comprising a duct formed of a sheet of material wrapped into cylindrical form, and a separate, rigid, ring-shaped flange attached to each end of the duct. 2) A fan casing as claimed in claim 1, in which each said flange comprises a cylindrical portion secured to the duct and an annular portion projecting radially-outwards from said cylindrical portion. 3) A fan casing as claimed in claim 2, in which the annular portion of each said flange is bent inwardly to an inclined position directed towards the cylindrical portion of that flange. 4) A fan casing as claimed in any preceding claim, further comprises a cross-member having its opposite ends secured to the duct and a fan unit mounted to said cross-member. 5) A fan casing as claimed in any preceding claim, in combination with a ring-shaped band for each said flange, each said band having an inner peripheral groove for fitting over a said flange of the fan casing duct and a corresponding flange on an end of a duct or assembly to which the fan casing is to be assembled.

Inventors: BIGGS COLIN, BIGGS, COLIN
Applicants: BIGGS COLIN, NUAIRE LTD, BIGGS, COLIN, NUAIRE LIMITED
Application year: 1994
Main classification: F24F13
IPC codes: F04D29, F16L23, F24F7, F24F13